The invention relates to fire break glazing units comprising an intumescent material with improved properties.
Fire break glazing of this type can lead to the use of different materials. The choice of intumescent materials has a significant influence not only on the thermal characteristics of the glazing but also on the production techniques of such glazing which in particular are one of the significant factors in their cost price.
The products demanded by users must have ever more effective properties. In particular, glazing units must be fire resistant for an increasingly long period in increasingly more severe temperature conditions. To meet these new demands, the manufacturers of such glazing units have proposed in particular the use of new intumescent materials with better resistance to very high temperatures. When evaluating the resistance of these materials, an important factor is the temperature at which the intumescent material melts or breaks down after formation of the foam in fire test cycles. This transformation in the material is associated with the loss of its is insulating properties. If the most usual intumescent materials, those based on hydrated alkaline silicates, transform at a temperature in the order of 400 to 500° C., other materials enable 700° C. to be reached and exceeded.
Of the materials, which lead to foams resistant to the most elevated temperatures, compositions containing phosphates are those which appear to respond best to these new demands. Materials of this type have been the subject of patent publications, in particular WO 99/19422 in the name of the Applicant. Apart from their increased thermal resistance, intumescent materials of this type differ from the most usually used silicate-based materials by their rheological properties and their conditions of use resulting from these. In particular, these phosphate-based compositions gel in very specific conditions, and do not always exhibit the required stability in thermal shock tests. The main difficulty is the tendency of phosphate-based intumescent materials to creep under the effect of the heat at temperatures lower than those at which the foam forms.
It is understood that the efficiency of fire break glazing requires that each of the constituents properly plays its role. Intumescent material contributes in various ways. It absorbs part of the heat received by the glazing by vaporizing the hydrating water it contains. It also forms a screen for thermal conduction and radiation via the opaque foam it forms during evaporation of this same water. Finally, the material holds the glass sheets in position even after they have been shattered by the thermal shock. If the material is removed by creep before causing the formation of foam, it cannot play any of these roles which are essential to the favorable functioning of fire break glazing.
In order to increase the fire behavior of glazing units, one measure currently used is to increase the number of glass sheets and intumescent interlayers. The principle is to successively oppose factors which accordingly slow down the final destruction of the glazing. In the case of an assembly comprising several layers of intumescent phosphate-based material, the difficulty may come from inadequate creep resistance at the temperatures preceding expansion. In fact, if during the fire test the thermal shock enables the first intumescent layer to expand properly, the temperature of the following layers “protected” by this first thermal barrier increases more slowly. If the intumescent material is not sufficiently resistant to creep at high temperature, the subsequent layers are not able to contribute satisfactorily.
Therefore, the inventors have sought to find improved intumescent materials which have a very high foam transformation temperature and at the same time are creep resistant at the intermediate temperatures preceding formation of the foam.